Klystron collector with inner serrated surface for reducing electron return



W. SCHMIDT April 20, 1965 KLYSTRON COLLECTOR WITH INNER SERRATED SURFACE FOR REDUCING ELECTRON RETURN 3 Sheets-Sheet 1 Filed May 23, 1962 I I a w Q HNVENTOR WOLFGANG $CHMIDT Apnl 20, 1965 w. SCHMIDT 3,179,839

KLYSTRON COLLECTOR WITH INNER SERRATED SURFACE FOR REDUCING ELECTRON RETURN Filed May 23, 1962 5 Sheets-Sheet 2 Fig.2

iNVENTOR WOLFGAQNG SCHMIDT 3L 4% miwi AGE April 20, 1965 w. SCHMIDT 3,179,839

KLYSTRON COLLECTOR WITH INNER SERRATED SURFACE FOR REDUCING ELECTRON RETURN Filed May 23, 1962 5 Sheets-Sheet 5 F ig.3

INVENTOR WOLFGANG SCHMIDT AGEN United States Patent 4 Claims. 61. 315 -538 The invention relates to an electron beam tube for velocity modulation (klystron) comprising a tubular electrode (drift tube) with a number of. sections separated by gaps which are bridged by cavity resonators, in which at one end of the drift tube there is provided a collector electrode insulated from the drift tube for direct current.

It is known to raise the efficiency of a klystron by connecting the collector electrode to a lower direct voltage with respect to the cathode than the drift tube and the cavity resonators. Since the velocity of the electrons in the electron beam, depending upon the energy output to the high-frequency fields in the cavity resonators may be materially reduced, electrons having different velocities emanate from the end of the drift tube and penetrate into the collector electrode. Since with a reduced direct voltage at the collector electrode between the end of the drift tube and the collector electrode a retarding field is produced, only the more rapid electrons can traverse this retarding field and be captured by the collector electrode. The slower electrons can be rejected by the retarding field in the drift tube, unless they are collected by taking particular precautions and, if certain phase relations are provided, they may give rise to unwanted oscillations.

Since with a view to improvement in efficiency the collector direct voltage is preferably chosen as low as possible, it is desirable to collect the reflected electrons as much as possible, before they can give rise to troublesome effects. It is already known to counteract the rejection of electrons by providing the entrance of the collector electrode with one or more grids arranged obliquely to the axis of the electron beam tube. However, such grids can be used at best only with low-power klystrons. With klystrons having a number of cavity resonators and a high power such grids are, however, unsuitable.

The invention has for its object to provide a high-power klystron in which the collector electrode is insulated from the drift tube for direct current, a structure by which rejection of the slow electrons to the cavity resonators is avoided.

In an electron beam tube for velocity modulation comprising a drift tube with a number of sections separated by gaps which are bridged by cavity resonators, in which at one end of the drift tube there is provided a collector electrode which is insulated from the drift tube for direct current, the end of the drift tube facing the collector electrode is, in accordance with the invention bevelled and surrounded by the entrance part of the collector electrode so that between the collector electrode and the end of the drift tube there is formed an oblique negative electrostatic lens.

. In accordance with the potential difference between the two electrodes of said lens and the velocity of the electrons are deflected laterally from their path so that the slowest electrons cannot penetrate into the collector electrode,

and the electrons of high velocity are slightly deflected,

it is true, but penetrate further into the collector electrode, where they are captured. The laterally deflected, slow electrons are collected within the bevelled end of the drift tube. The velocity at which the electrons are still laterally deflected and projected onto the drift tube depends 3,1795% Patented Apr. 20, 1965 upon the angle of deflection and the potential difference.

In accordance with the invention the deflection of the electrons may be enhanced by means of an external magnetic field at right angles to the axis of the tube and to the direction of deflection.

In order to avoid that secondary electrons produced by rejected electrons striking the drift tube should assume initial velocities towards the cavity resonators, there are provided, in accordance with the invention, grooves in the bevelled end of the drift tube so that the sectional area of the drift tube has a sawtooth-like form, the points being orientated towards the collector electrode. Moreover, in accordance with the invention the surface of the drift tube and/ or of the collector electrode may have poor secondary'emission properties, if necessary by means of a separately applied layer.

The invention will now be described more fully with reference to the accompanying drawing, in which FIG. 1 shows diagrammatically the relative positions of the end of the drift tube and the collector electrode of a known klystron,

FIG. 2 shows the same diagram for a klystron according to the invention and FIG. 3 shows the arrangement of magnets producing the magnetic field in order to obtain an additional deflection.

In FIG. 1 the electron beam traversing the klystron is indicated by the arrow 1. Between the two parts 2 and 7 of the drift tube the last cavity resonator 3 is arranged. The drift tube part '7 is followed by the collector electrode 5, having a front wall 4. The entrance of the collector electrode is designated by 11. Owing to the potential difference between the drift tube end 7 and the collector input 11 a retarding field 17 is produced between the ends 13 and 15 thereof. The high-velocity electrons 19 follow the paths 20, which are deflected not until inside the collector electrode 5. The slow electrons 21, which have given off the major part of their kinetic energy to the high-frequency fields in the cavity resonators, cannot, however, traverse the retarding field 17 and, as is indicated by the paths 22 (broken lines), they return towards the cavity resonators, so that the klystron may start oscillating in an undesirable manner.

As is shown in FIG. 2 the rejection of the slow electrons is avoided by bevelling the drift tube end 7 with respect to the axis 23 of the tube along the plane 25 so that this end is at an angle a to the axis 23 of the tube. Moreover, said end 7 of the drift tube is surrounded by the entrance end 11 of the collector electrode. Therefore, between the plane 25 and the tube 11 there is produced a negative electro-static lens 27, which exerts a strongly deflecting effect on the slow electrons so that the slow electrons are projected onto the inner side of the end '7.

The inner side of the drift tube end 7 is provided with machined rims 33 having sharp points 35, so that a sawtooth-like sectional area is formed, the points being orientated towards the collector electrode. Thus secondary electrons 29 produced on the wall emanate always in the direction of the collector. The entrance 11 of the collector electrode and the end 7 of the drift tube, which are coaxial relatively to each other, are surrounded by a cylinder 37, connected with the drift tube and arranged at a fairly small distance therefrom, so that a capacitor is formed, which constitutes a capacitative short-circuit for the high-frequency voltages between the end of the drift tube and the collector electrode. The magnets 39 shown in FIG. 3 produce a magnetic field at right angles What isclairned is:

1. In a velocity-modulated electron beam discharge tube a drift tube having a plurality of sections separated by gaps, a cavity resonator bridging at least one of said gaps, a collector electrode spaced from and having a portion surrounding one end of said drift tube, said collector being direct-current electrically insulated from said drift tube, said end of said drift tube surrounded by said collector'electrode portion being bevelled and having a plurality of serrations on the inner surface thereof with the points of said serrations oriented towards the collector electrode to thereby form between the collector electrode and the drift tube an oblique, negative electrostatic lens.

2. An electron beam tube as claimed in claim 1, in which an external magnetic field is provided at right angles to the axis of the tube and at right angles to the direction of deflection of the electrons.

References Cited by the Examiner UNITED STATES PATENTS 2,250,511 7/41 Varian et a1, 3l55.38 X 2,445,811 7/48 Varian 315-438 X 2,774,913 12/56 Charles 315-35 X 2,804,569 8/57 Huber 315 3.5 X 3,036,237 5/62 Zitelli et al. 315-535 v ROBERT SEGAL, Acting Primary Examiner. DAVID J. GALVIN, Examiner. 

1. IN A VELOCITY-MODULATED ELECTRON BEAM DISCHARGE TUBE A DRIFT TUBE HAVING A PLURALITY OF SECTIONS SEPARATED BY GAPS, A CAVITY RESONATOR BRIDGING AT LEAST ONE OF SAID GAPS, A COLLECTOR ELECTRODE SPACED FROM AND HAVING A PORTION SURROUNDING ONE END OF SAID DRIFT TUBE, SAID COLLECTOR BEING DIRECT-CURRENT ELECTRICALLY INSULATED FROM SAID DRIFT TUBE, SAID END OF SAID DRIFT TUBE SURROUNDED BY SAID COLLECTOR ELECTRODE PORTION BEING BEVELLED AND HAVING A PLURALITY OF SERRATIONS ON THE INNER SURFACE THEREOF WITH THE POINTS OF SAID SERRATIONS ORIENTED TOWARDS THE COLLECTOR ELECTRODE TO THEREBY FORM BETWEEN THE COLLECTOR ELECTRODE AND THE DRIFT TUBE AN OBLIQUE, NEGATIVE ELECTROSTATIC LENS. 